Comparison of blind, ultrasound- and neurostimulator-guided methods of percutaneous inferior alveolar nerve block

Background: An inferior alveolar nerve block is often utilised for anaesthesia of the mandibular arcade of teeth prior to dental procedures. It has been described with multiple approaches and methods; however, at the current time, no direct comparison of percutaneous methods is available. Objectives: To compare the accuracy of percutaneous infiltration of the inferior alveolar nerve with a ventral blind approach (control) to blind caudal approach, ultrasound-guided and neurostimulator-guided methods. Study design: Prospective comparison of methods using anaesthetised horses prior to euthanasia or cadavers, being utilised for another study. Methods: An 18 G spinal needle was used to inject a volume of 1 ml, composed of 0.5 ml of methylene blue and 0.5 ml of iodinated CT contrast medium, with placement guided by the aforementioned methods. Following injection the needle was left in place, CT-imaging was performed and then the skulls were dissected. CT enabled assessment of the coverage of the mandibular foramen with contrast medium and distance of the needle tip from the mandibular foramen and dissection enabled assessment of the staining of the inferior alveolar nerve and lingual nerve. Results: The highest percentage of contrast staining of the inferior alveolar nerve and coverage of the mandibular foramen at CT was achieved with caudal blind and ultrasound-guided approaches; however, no group reached a significant difference to control (ventral blind approach). Concurrent staining of the lingual nerve (possibly associated with undesired side effects) had high incidence and was similar between groups. Main limitations: Use of horses under anaesthesia/cadavers does not replicate clinical conditions and staining/coverage is assumed to relate to a clinically effective block. Conclusions: Ultrasound-guided and caudal approaches did have increased percentage of successful staining, but neither reached significance compared to the ventral blind approach.